1. Field of the Invention
The present invention relates to a technology for use with an image pickup apparatus, and more specifically to a controlling technology for use with an image pickup apparatus in the single-lens reflex system which captures a subject image captured through finder optics by forming the image on the surface of an image pickup device through pickup optics.
2. Description of the Related Art
A digital camera is well known with its configuration of finder optics and pickup optics for capturing a subject image obtained through the finder optics and forming the image on the surface of the image pickup device through the pickup optics. With this type of camera, it is desired that the scope visually identified within the view frame in the finder optics strictly matches the scope of the captured image actually recorded by the camera. A desired view ratio obtained by dividing the scope within a view frame by the scope of a captured image as represented on a percentage basis is 100%.
However, actually in the production process of a digital camera, a delicate alignment error occurs in setting a view frame and an image pickup device. Therefore, to suppress the occurrence of a case in which a part of an image in the view frame cannot be recorded due to the alignment error, a reduced view frame is set with an alignment error taken into account. Therefore, the view ratio obtained by the digital camera using the above mentioned view frame has been about 95% at most.
To improve the view ratio, there is a method of minutely controlling the alignment between the view frame and the image pickup device in the production process of a digital camera. However, in this method, the production cost soars by the alignment control. Furthermore, for example, if a CCD (charge coupled device) is used, then a precision error (±0.15 mm approximately) occurs in the fixed position of the CCD in its parts package, and the similar precision error occurs in the outer shape of the parts package, thereby making it more difficult to specify a reference position for alignment control, and presenting the most difficult controlling operation.
Relating to the technology of reducing the displacement between the scope visually identified within the view frame set by the finder optics and the scope of a captured image actually recorded by the pickup optics, Japanese Patent Publication No.8-304910 discloses the invention of computing the amount of displacement of a view based on the measurement result of a distance to a subject and providing an area segmented from a capture area based on the computation result as a printing screen, thereby substantially matching the view area with the area displayed on the printing screen so that the displacement occurring between the view area and the capture area obtained by different optics, and changing in amount depending on the distance to a subject, which is referred to as parallax, can be corrected. However, the invention has the problem of the high cost and the heavy devices because it requires exclusive hardware for computing the amount of displacement of a view or a program for computing a general-purpose arithmetic device in the image pickup apparatus. Furthermore, the invention has to compute the amount of displacement if a view each time a capturing process is performed, thereby causing the problems of the response in the capturing process, and the power consumption. Additionally, the parallax also occurs in the camera in which the finder optics and the pickup optics are different optics. This parallax problem does not practically occur in the single-lens reflex system in which the finder optics and the pickup optics share optics with each other.